The present invention relates to a method of fabricating a diffraction grating and a diffraction grating.
Conventionally, a diffraction grating is fabricated in such a manner that, for example, as shown in FIG. 1, an optical mask 5 having a mask substrate 1 and a light shielding film 3 having a predetermined pattern formed on the mask substrate 1, and a resist substrate 11 having a substrate 7 and a resist layer (photosensitive material) 9 formed on the substrate 7, are prepared, respectively, the resist substrate 11 is put on the optical mask 5, and a luminous flux of exposure light (arrows) is vertically irradiated from the optical mask 5 side and after that, development is conducted on the same side as that of exposure.
However, since an air layer or a vacuum layer inevitably exist between the light shielding film 3 and the resist layer 9, noise light is generated by interfacial reflection during the exposure process, and a portion which must not be originally exposed to light is exposed to the noise light. Therefore, it is very difficult to fabricate, for example, a highly accurate diffraction grating, a diffraction grating of a fine profile and a diffraction grating the cross-section of which is oblique.
It is an object of the present invention to provide a method of fabricating a diffraction grating capable of effectively suppressing generation of noise light, by reducing or eliminating interfaces.
It is another object of the present invention to provide a diffraction grating having a new cross-sectional shape having a high diffraction efficiency.
In order to solve the above problems, a method of fabricating a diffraction grating by utilizing a single substrate, according to the present invention, comprises the steps of: forming a photosensitive material layer and a light transmission reducing film having a predetermined pattern integrally with each other on the substrate; exposing the photosensitive material layer by exposure to light via the light transmission reducing film; and developing the photosensitive material layer after exposure.
Preferably, the photosensitive material layer is provided on one side of the substrate and the light transmission reducing film is provided on the other side of the substrate. Preferably, the photosensitive material layer and the light transmission reducing film are provided on the same side of the substrate. Preferably, a reflection preventing layer is provided outside the photosensitive material layer. Preferably, a method of fabricating a diffraction grating further comprises the steps of: plating a surface of the photosensitive material layer after development; and fabricating a diffraction grating by utilizing the plated photosensitive material layer as a master grating. Preferably, a method of fabricating a diffraction grating further comprises the steps of: pouring resin onto a surface of the photosensitive material layer after development; curing the poured resin; and removing the cured resin.
A photosensitive substrate, according to the present invention, has a light shielding film having a predetermined pattern formed on one side thereof and a photosensitive material layer formed on the other side thereof.
A further photosensitive substrate, according to the present invention, has a light shielding film having a predetermined pattern formed on one side thereof and a photosensitive material layer formed on the light shielding film.
A diffraction grating is formed parallel to and on a predetermined substrate at a predetermined pitch, according to the present invention, wherein a root portion of each diffraction grating in cross-section is constricted.
Preferably, in cross-section of each diffraction grating, a portion from the root to the forward and is entirely oblique. Preferably, in cross-section of each diffraction grating, a forward end portion is formed into a profile in which rectangles are overlapped.